When a fan blows air across a room, the airflow typically decelerates and spreads out. Now in a new study, scientists have demonstrated the opposite: an airflow created by a carefully controlled ultrasound array can maintain its narrow shape and accelerate as it moves away from the source. The researchers explain that it’s as if the airflow is being pushed along by a sequence of invisible fans floating in mid-air. They expect that the accelerating air stream could have unprecedented applications, such as the ability to perform and control chemical reactions in mid-air.